Today's wireless communication systems generally use a single radio frequency (RF) band, having a bandwidth anywhere from less than 5 MHz to over 200 MHz, to transmit and receive data. These wireless communication systems are generally capable of transmitting multiple RF carriers in one RF band.
The Federal Communications Commission (FCC) in the United States, and their equivalent organizations in other countries, continue to free up new RF bands, which is creating new requirements for both industry standards organizations, such as the 3rd Generation Partnership Project (3GPP) and cellular operators, for advanced wireless communication systems that can efficiently use these new RF bands.
Today's wireless communications standards generally utilize two multiplexing techniques. For example, the GSM and CDMA standards utilize Frequency Domain Duplex (FDD) multiplexing techniques. The WiFi and WiMAX standards utilize Time Domain Duplex (TDD) multiplexing techniques and use a single RF carrier in one RF band. New developments in wireless communications standards that use TDD multiplexing, such as WiFi (802.11ac) and Long-Term Evolution (LTE), specify the transmission and reception of data over multiple RF bands where each RF band has one or more RF carriers. The multiple RF carriers may be contiguous in one RF band (i.e., intra band contiguous), non-contiguous in one RF band (i.e., intra band non-contiguous,) or non-contiguous in two RF bands (i.e., inter band non-continuous). FIG. 1A shows three contiguous RF carriers in a single RF band, or intra-band; FIG. 1B shows two contiguous RF carriers and one non-contiguous RF carrier in a single RF band, or intra-band; and FIG. 1C shows two contiguous RF carriers in a first RF band and one RF carrier in a second non-contiguous RF band, or inter-band.
A “brute force” method that is typically used to adapt conventional wireless communication systems to accommodate the requirements of new multi-band wireless communications standards involves implementing separate transceivers for each RF band and transmitting and receiving data in each RF band using a single radio. The “brute force” method, however, limits the ability of an operator of the wireless communications systems to manage power consumption of the radio.
Examples of known multiband and multicarrier wireless communication systems that are capable of transmitting and receiving data in two RF bands using one or more RF carriers are shown in FIG. 2A and FIG. 2B. FIG. 2A and FIG. 2B each show a conventional multiband and multicarrier wireless communication system 200 that includes a baseband unit 202 connected to two separate RF transceivers 204, 206 by optical cables 208, 210. The two RF transceivers 204, 206 are in turn connected to a single multi-band antenna 212 by two RF coax cables 214, 216, respectively. The difference between conventional multiband and multicarrier wireless communication system shown in FIG. 2A and the one shown in FIG. 2B is that the two RF transceivers 204, 206 are packaged into a single box 218 in the conventional multiband and multicarrier wireless communication system shown in FIG. 2.
Each RF transceiver in a conventional multiband and multicarrier wireless communication system, such as those shown in FIG. 2A and FIG. 2B, includes analog-to-digital converters (ADCs) for converting RF signals between the analog and digital domains, and digital-to-analog-converters (DACs) for converting RF signals between the digital and analog domains. When converting an analog signal to the digital domain, to accurately represent that signal it must be sampled at a frequency between 2 to 5 times the bandwidth of the RF signal. Nyquist theory states that sampling at 2 times the bandwidth of the RF signal is required; however often up to 5 times the bandwidth of the analog RF signal is used in order to cancel out harmonics. Changes in wireless standards have resulted in wireless signals increasing in bandwidth that non-contiguously span intra-band and inter-band frequency ranges, requiring ADCs and DACs with increasing sampling rates. These ADCs and DACs are expensive and inefficient in the use of electrical power. Furthermore, the sampling rates of ADCs and DACs are unlikely to keep pace with the demands placed upon them by the evolving wireless standards.
Improvements in the conversion of wideband analog RF signals to the digital domain in multiband and multicarrier wireless systems are therefore desirable.